Alzheimer's Diagnostic Accuracy: Theory vs. Reality

Contributed by: Dennis Fortier, President, Medical Care Corporation

The reports on diagnosing Alzheimer's disease are maddeningly conflicting.

Research in academic journals makes it clear that a primary care physician can achieve a high level of diagnostic accuracy by following published guidelines.  However, journalists report every day that Alzheimer's disease can only be definitively diagnosed with an autopsy.  So which is it?

It turns out that both statements are correct.

Definitive vs. Clinically Acceptable
It is technically true that an autopsy is required for a "definitive diagnosis".  However, in the world of practiced medicine, we rarely operate with definitive diagnoses for any disease or condition.  Instead, we rely on "clinically acceptable" diagnoses that are accurate about 85%-95% of the time.  The emphasis on "definitive", or 100% accuracy, is actually quite misleading since it establishes an unrealistic standard that is rarely met in the real world of medical practice.

As for the academic perspective, a clinically acceptable level of accuracy is indeed achievable by following published guidelines.  These guidelines involve a complete medical history including a review of medicines, neuro-psychological assessment, blood tests, and an MRI or CT image of the brain.  In some cases, a PET scan of the brain might also be required.

Diagnostic Guidelines
To paraphrase the guidelines: if a patient shows impaired short-term memory as well as impaired cued recall, is not taking any medications known to disturb memory, is not abusing alcohol or other drugs, is not depressed or suffering from anxiety, does not have any apparent or detectable infections, has no uncontrolled diabetes or hypertension, has a properly functioning thyroid and no particular vitamin deficiencies, has not suffered a recent head trauma, and has no evidence of strokes or tumors in the brain, then the physician can be quite confident that the patient has Alzheimer's disease.

Essentially, the hallmark forms of memory impairment need to be objectively confirmed by cognitive assessment, and other known causes of such impairment ruled out.  A family history of Alzheimer's disease, or a genetic test showing a particular predisposition, would add confidence to such a diagnosis.

Why the Different Perceptions?
The reason for the stark difference in the academic perception of diagnostic accuracy and the journalistic perception of diagnostic accuracy is "lag".  In this case, lag refers to the well documented time-gap between medical advance and implementation of medical advance.  In other words, medical research leaps forward much faster than physicians can learn about and implement new findings and guidelines.  Right now, there is a significant gap between best practices in the field of memory loss and the actual practices that physicians are using in their clinics.

Half of Alzheimer's Cases Misdiagnosed
Recent articles from CNN and WebMD have reported that about half of Alzheimer's cases may be misdiagnosed in clinics.  Oddly, this probably indicates progress from recent years when memory problems went largely undiagnosed and ignored, to current times when many memory problems are being improperly attributed to Alzheimer's disease.  Progressing from "doing nothing" to "doing the right thing half the time" is actually a favorable development.

With time, our over-worked physicians will gain a better command of emerging guidelines.  This will improve their collective ability to recognize problems and to accurately determine their cause before prescribing treatment.

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